European patent application publication number 2 422 048 discloses a pump comprising a housing, the housing having an interior defining a rotor path, an inlet formed in the housing at a first position on the rotor path, an outlet formed in the housing at a second position on the rotor path spaced from the first position, and a rotor rotatable in the housing. At least one first surface is formed on the rotor and seals against the rotor path of the housing, and at least one second surface is formed on the rotor circumferentially spaced from the first surface and forming a chamber with the rotor path that travels around the rotor path on rotation of the rotor to convey fluid around the housing from the inlet to the outlet. A resilient seal is located on the rotor path and so extends between the outlet and the inlet in the direction of rotation of the rotor such that the first rotor surface seals with, and resiliency deforms, the seal, as the rotor rotates around the rotor path within the housing to prevent fluid flow from said outlet to said inlet past the seal.